In any cellular mobile communication system, such as a GSM network, mobility management, i.e. the location of subscribers or mobile stations is handled on different levels. At the topmost level, the home location registers (HLR) hold data on which part of a network a mobile subscriber is roaming in and also which visitor location register (VLR) the mobile subscriber is currently registered with. Visitor location registers (VLR) hold data on which location area (LA) a mobile subscriber is currently in. A location area is controlled by a mobile switching center (MSC) and a number of base station controllers (BSC) and is divided into several cells each representing the coverage area of a base station transceiver (BTS). The location area is broadcast in each cell by the base transceiver station BTS. A roaming mobile station is thus able to detect when it moves from one location area to the next and can inform the visitor location register VLR. However, if the mobile station simply moves from one cell to another within the same location area the visitor location area is not informed. This means that in order to locate a mobile station within the network the core network knows only which location area the mobile is in and must page the mobile in all cells within this location area.
Conventional cellular networks can be extended by adding access networks that utilise a low power unlicensed-radio interface to communicate with mobile stations. These access networks are designed to be used together with the core elements of a standard public mobile network and consist essentially of plug-in low-power unlicensed radio transceivers, or access points, each designed to establish an unlicensed radio link with a mobile station MS and a controller or interface node connecting the unlicensed radio transceivers with the mobile core network. Suitable unlicensed-radio formats include digital enhanced cordless telecommunications (DECT), wireless LAN and Bluetooth. An adapted mobile handset capable of operating over both the standard air interface (e.g. the Um interface) and the unlicensed-radio interface means that the subscriber requires only one phone for all environments. The access network is constructed so that the core elements, such as the mobile switching centers MSC, of the public mobile network views the interface node as a conventional base station controller BSC. Such an access network and the mobile station for use with this access network are described in European patent application No. EP-A-1 207 708.
The low power and resultant low range of the unlicensed-radio interface means that several such access networks may be provided in relatively close proximity, for example one access network per floor of an office building or in a private home. The connection between the unlicensed-radio transceivers and the associated controller is preferably provided by a fixed broadband network. Preferably communication over this network uses the internet protocol IP, which greatly facilitates the installation of the access network, permitting a subscriber to plug-in an unlicensed-radio transceiver in his own home and even move it temporarily to an alternative location and consequently install an unlicensed-radio access point himself. The combination of the small size of the access point coverage areas and the ease with which it can be installed and moved means that each access point controller will be controlling a very large but frequently changing number of cells compared to the equivalent base station controller of a conventional cellular network. Consequently when a mobile station roaming somewhere in the unlicensed radio access network must be paged by the core network, the signalling load on the access point controller will be very high due to the large number of cells and access points implicated.